Fear gripped Nigeria on Monday after a wave of Christmas bombings blamed on Islamists killed at least 40, including worshippers who were left begging for mercy as they exited a church.

Hundreds of residents sought to flee the violence-torn city of Damaturu on Monday fearing further attacks and clashes between Islamists and police, while some 30 Christian shops were burnt in the nearby city of Potiskum late Sunday.

At the damaged St. Theresa Catholic Church in Madalla near the capital Abuja where the bloodiest attack took place, a special mass was held in memory of the 35 victims there despite splattered blood still visible on the outside.

“I have never cried before,” Father Isaac Achi told the audience of several hundred which included bishops and priests from the region as well as the Vatican’s representative to Nigeria.

“Yesterday I cried. This morning I cried. But with all of you around today, I will not cry again. Seeing you coming to say this mass, I’m telling you, I will not cry again.”

The blast struck as the service was ending and worshippers were filing out.

Some of the wounded, including one man whose entrails protruded from his body, ran toward a priest for final blessings. Some were burnt in their cars.

Nigeria has seen scores of attacks claimed by Islamist group Boko Haram, but some analysts said the bombings marked a dangerous escalation in a country divided between a mainly Muslim north and predominantly Christian south.

The government in Nigeria, Africa’s most populous nation and its largest oil producer, blamed Islamist sect Boko Haram for three attacks on Sunday.

In the central city of Jos, a church was targeted and a policeman was killed in a resulting shootout.

A suicide blast also occurred in the restive northeastern city of Damaturu when the bomber sought to ram into a military convoy in front of a secret police office, killing himself and three security agents.

A third church was targeted in the northeast on Christmas Eve, but no one was reported killed. Residents reported another explosion near a church in the northeastern city of Maiduguri late Sunday, but an army spokesman denied it.

In Damaturu on Monday, hundreds of residents sought to flee, lining up at taxi and bus stands amid momentary calm.

“The situation in the city is frightening,” said a 42-year-old trader with his wife and three young children as he waited along the roadside. “You never can tell where will be the next target. My house was burnt in the attacks.”

In the nearby city of Potiskum, residents and a police source said about 30 Christian shops burned on Sunday night, while a supermarket and the home of a local Christian leader were also set ablaze.

Some worried the attacks could set off a new round of sectarian clashes.

“The attack on churches is to nationalise the crisis,” said Shehu Sani, a rights activist based in Nigeria’s north.

“It will instigate hitherto neutral people into the crisis. Christians may want to take revenge on Muslims and this is dangerous for the country.”

There has been intense speculation over whether Boko Haram has links with outside extremist groups, including Al-Qaeda’s north African branch.

The attacks drew widespread condemnation, including from the Vatican, UN chief Ban Ki-moon, the United States and Britain.

“I wish to express my solidarity with those who have been hit by this absurd act,” Pope Benedict XVI told a crowd gathered for his Angelus prayer, adding that he was “deeply saddened” by the attacks.

President Goodluck Jonathan condemned the attacks and pledged to bring the attackers to justice, but the government has so far been unable to stop the Islamists, whose attacks have grown increasingly sophisticated and deadly.

While the government blamed Boko Haram and a purported spokesman for the sect claimed responsibility, conflicting accounts emerged.

A spokesman for police in Niger state, where Madalla is located, said authorities had not yet determined who was behind the attack.

“We are looking beyond Boko Haram because other people bent on destabilising the government might be doing these things in the name of Boko Haram,” said Richard Oguche.

Describing the bombing, National Security Adviser Owoye Azazi said attackers threw improvised explosive devices from a moving vehicle, adding that “two of the criminals had been apprehended, caught in action.”

Oguche said no one was arrested and the blast occurred after a minibus pulled up near the church. He added that three police officers were among those killed.